The calcined powders mentioned above were subsequently granulated with BRL 50481 polyvinyl alcohol (PVA) binder and pressed into pellets with 12 mm in diameter and 1.5 mm in thickness. The pellets were first heated at 600 °C for 2 h to drive off PVA, and then sintered at temperatures between 1050 and 1200 °C for 2 h to produce xBA–(1 − x)BT ceramics or Nb-doped 0.2BA–0.8BT ceramics.
3. Results and discussions
3.1. TG–DSC and XRD for 0.2BA–0.8BT powders
Fig. 2. The TG–DSC patterns of the xBA–(1 − x)BT pre-calcined powders prepared by solid-state reaction method (a) and sol–gel method (b).Figure optionsDownload full-size imageDownload as PowerPoint slide
The X-ray diffraction patterns of 0.2BA–0.8BT powders calcined at different temperatures were used to check calcination temperature judging from TG–DSC. As seen in Fig. 3a, although the perovskite phase could be formed at temperature as low as 850 °C, the crystallinity was slightly low, as indicated by the broad diffraction peaks. Instead, the sample calcined at 900 °C or higher temperatures showed quite well defined diffraction peaks. Additionally, in Fig. 3b, translation is easy to observe a broad peak located in the range of 25–35° when calcined at 600 °C, as a result of incompletely crystallizing. But the perovskite phase could be observed when sample calcined at ≥700 °C. Therefore, the minimum calcination temperatures of solid-state reaction method and sol–gel method were 900 °C and 700 °C.